A large number of genes are known which are expressed only in developing seeds, or are expressed in developing seeds at much higher levels than in any other organ or tissue type. Much of the information about seed-specific gene expression has been derived from studies of genes encoding storage proteins (reviewed by Bevan et al., Phil. Trans. Royal Soc. Lond. Biol. Sci., 342:209-215 (1993)). For instance, DNA sequences that confer embryo-specific expression by the soybean conglycinin promoter in transgenic plants have been identified (Chen et al., EMBO J., 6:3559-3564 (1988)). Similarly, the storage protein napin is one of the major protein components of Brassica napus L. (oilseed rape) seeds. The 5′ regulatory region from napin has been published (Kridl et al., Seed Sci. Res., 1:209-219 (1991)). A 152 bp fragment from the napin promoter directed strong expression of the β-glucuronidase reporter gene in mature tobacco seeds (Stalberg et al., Transgenic Research, 7(3): 165-172 (1998)). The napin promoter has been used to control expression of genes in transgenic plants designed to produce novel fatty acids (e.g., Voelker et al., Plant Journal, 9:229-241 (1996)). However, because storage lipid accumulation begins substantially before the maximal level of expression of the napin or other storage protein genes is reached (Post-Beittenmiller et al., in Control of Plant Gene Expression. Verma, D. P. (ed.) Telford Press, pp. 157-174 (1992)), the promoters of storage protein genes may not always be preferred for controlling expression of genes related to oil accumulation in plant seeds.
Current technology permits the transformation of plants with heterologous genes. The expression of these genes is either ubiquitous if the promoter is constitutive, or is regulated in a temporal or spatial manner if the promoter is stage- or tissue-specific. Continuous expression precludes production at particular stages or in specific tissues, and can adversely affect yield due to increased energy demands associated with prolonged synthesis of the product. Tissue- or stage-specific expression permits greater control over the temporal and spatial accumulation of desired products. Thus, promoter sequences that control the expression of desired genes in a tissue-specific, stage-specific manner that can be employed in recombinant constructs for the transformation of plants, and that would facilitate greater control over the location, timing, and duration of expression of introduced genes and reduce the possibility of deleterious effects on overall plant growth, are highly desirable.
For production of transgenic plants with various desired characteristics, it would be advantageous to have a variety of promoters to provide gene expression such that a gene is transcribed efficiently in the amount necessary to produce the desired effect. The commercial development of genetically improved germplasm has also advanced to the stage of introducing multiple traits into crop plants, often referred to as a gene stacking approach. In this approach, multiple genes conferring different characteristics of interest can be introduced into a plant. It is often desired when introducing multiple genes into a plant that each gene is modulated or controlled for optimal expression, leading to a requirement for diverse regulatory elements. In light of these and other considerations, it is apparent that optimal control of gene expression and regulatory element diversity are important in plant biotechnology.